Method for selecting frequency channels

ABSTRACT

A method selects frequency channels in a communication system using a frequency hopping method, in which data are transmitted between a transmitter and a receiver. The data are transmitted as data packets having a plurality of bits in a frequency/time block. A respective data packet is coded before transmission by the transmitter and is decoded after reception by the receiver. The transmission quality of the frequency channels is evaluated and, a decision is made for a selection of the frequency channel which is used for the transmission of the data. A likelihood ratio for the likelihood of a successful transmission is determined before the decoding by the receiver, the likelihood ratio is used as a metric for determining the interference state of the respective data packet, and the transmission quality of the respective frequency channel is evaluated on the basis of the interference state of the data packet.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of patent application Ser. No.16/287,258, filed Feb. 27, 2019; which was a § 371 national stage filingof international application No. PCT/EP2017/000983, filed Aug. 16, 2017,which designated the United States; the prior applications are herewithincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method for selecting frequencychannels in a communication system using a frequency hopping method.

Communication systems in which data are transmitted by a radio link areused today in many areas. For example, in the field of intelligentconsumption metering devices, known as smart meters. This concernsconsumption metering devices located in a supply network, e.g. forenergy, power, gas, water or the like, which indicate the actualconsumption to the respective connection user and are incorporated intoa generic communication system in order to transmit e.g. the recordedconsumption data to the provider. Intelligent consumption meteringdevices offer the advantage that manual meter readings are no longerrequired and shorter-term billing can be implemented by the provideraccording to actual consumption. Shorter-term reading intervals in turnenable a more accurate linkage between end customer tariffs and thedevelopment of trading prices for electricity. Supply networks can alsobe substantially more effectively utilized.

Intelligent consumption metering devices are normally assigned in eachcase to residential units or residential buildings. The consumption datagenerated there can be transmitted, for example, in the form of datapackets or parts of data packets (known as hops) via a radio link, e.g.in the ISM (Industrial, Scientific, Medical) or SRD (Short Range Device)band frequency range. These frequency ranges offer the advantage thatoperators require only a general license for frequency management.However, the problem exists that interference can often occur due to thefrequency of use of frequency ranges of this type for a wide range oftechnical devices, such as, for example, garage door controls, alarmsystems, WLAN, Bluetooth, smoke detectors, etc. Consumption data arenormally collected via a radio link either by stationary or mobilereceivers, referred to as data collectors or data concentrators, towhich the consumption data provided by the consumption metering devicesare transmitted. The data collectors can then forward the data to ahigher-level central unit, such as e.g. the central control room of theprovider.

Data packets can be transmitted in a communication system on a pluralityof frequencies or frequency channels within a frequency range (frequencyhopping method) in order to improve the transmission quality of the datapackets. The facility exists here to select frequency channels in atargeted manner, i.e. to eliminate interference-affected frequencychannels and transmit via frequency channels unaffected or less affectedby interference. A frequency channel changeover is performed accordingto the frequency hopping method if the data transmission on onefrequency channel is affected by interference.

A changeover to other frequency channels is preferably performedautomatically using the adaptive frequency hopping method. The adaptivefrequency hopping method enables a rapid response to frequency channelsaffected by interference. Furthermore, in the case of a frequencychannel changeover from a frequency channel affected by interference toa new frequency channel unaffected by interference, the new frequencychannel is defined by pseudorandom numbers. However, due to this randomselection of the new frequency channel, it may occur that a frequencychannel is selected which is similarly affected by interference or whosetransmission quality is even worse than that of the original frequencychannel.

A method for selecting frequency channels of a data transmission systemis known from German patent DE 103 20 176 B3, corresponding to U.S. Pat.Nos. 8,537,877 and 7,529,288. In the method, the transmission qualitiesof the frequency channels are determined during the transmission of adata packet between a transmitter and a receiver by measuring the datapacket error rate and/or the bit error rate, and also the field strengthof the received signal. The determined field strength is compared with adefinable threshold value field strength for the selection decision inrespect of the frequency channels. The data packet error rate and/or thebit error rate and also the field strength of the received signal aremeasured here within defined transmit timeslots of the measuring unit(transmitter or receiver) in which only one transmitter in each casetransmits data packets. The method is complex and susceptible tointerference, given that that the transmit timeslots have to becoordinated for all transmitters and receivers.

A method for operating a communication network is known from U.S. patentpublication No. 2002/0136268 A1. The communication network uses afrequency hopping method in which the performance of a communicationchannel or frequency channel is evaluated using different methods inorder to make a selection of the communication channel. For example, aspecific test packet with known content is transmitted via thecommunication channel, a received signal strength indicator (RSSI) isdetermined, a preamble correlation is carried out on the basis of apreamble at the beginning of the data packet, a packet loss ratio (PLR)is determined or a specific check is carried out, e.g. a header errorcheck (HEC), a cyclic redundancy check (CRC) or a forward errorcorrection (FEC) in order to test the performance of the communicationchannel.

U.S. patent publication No. 2006/0133543 A1 discloses a wirelesscommunication system using a frequency hopping method in which thefrequency channels are evaluated and selected on the basis of thereceived signal strength indicator (RSSI) or a packet error ratio (PER).

An apparatus for communicating via a radio communication channel isfurthermore known from U.S. patent publication No. 2006/0013172 A1, theapparatus using a frequency hopping method and carrying out a frequencychannel measurement and frequency channel selection here on the basis ofthe received signal strength indicator (RSSI) of a data packet receivedon the frequency channel.

A method for decoding a coded data packet is known from published,non-prosecuted German patent application DE 10 2013 008 253 A1,corresponding to U.S. Pat. No. 9,197,365. The data packets are decodedhere in such a way that they contain error detection bits (cyclicredundancy check (CRC) bits) and/or error correction bits (forward errorcorrection (FEC) bits). The receiver comprises a receiver module forreceiving the coded data packets, a decoder for decoding the datapackets, and an LLR module for defining LLR values, known as loglikelihood ratios, for coded data bits of the data packet. Here, the LLRvalue indicates the likelihood of the respective coded data bit beingaffected or unaffected by interference. A preselection determiningwhether or not the decoder decodes the data bits can finally be made onthe basis of these LLR values. The decoder can then detect and correctthe non-decoded data bits during the decoding on the basis of the errordetection bits and error correction bits.

SUMMARY OF THE INVENTION

On the basis of the prior art, the object of the present invention is toprovide a method for selecting frequency channels with which an improvedtransmission quality and transmission reliability are enabled.

The aforementioned object is achieved by the overall teaching of theindependent claim and of the subordinate claims. Appropriate designs ofthe invention are claimed in the subclaims.

According to the invention, a likelihood ratio (LR) is determined forthe likelihood of a successful transmission before the decoding by thereceiver. To do this, the receiver may, for example, have an LLR moduleto determine the LLR value of the data packet. The likelihood ratio LRis used here as a metric for determining the interference state of thedata packet, i.e. the likelihood ratio LR of the data packet serves e.g.as a numerical measure for determining the interference state of thedata packet. In a practical manner, the transmission quality of therespective frequency channel can thus be evaluated on the basis of thedetermined interference state of the data packet or the LLR values. Theselection of the frequency channels can thereby be improved in terms oftheir transmission quality to a particular extent, as a result of whichthe transmission quality and transmission reliability of thecommunication system can be substantially increased.

The likelihood ratio LR can be determined on a bit-by-bit basis, or fora defined number of bits of the data packet or of a part of the datapacket. The LLR module can, for example, determine an LLR value for eachtransmitted bit. The likelihood ratios LR of the bits determined in thisway or the defined number of bits can then be used as a metric fordetermining the interference state of the respective data packet or ofthe respective part of the data packet.

The signal power SL1 is appropriately determined in a frequency/timeblock outside the transmission of the respective data packet, i.e. thesignal noise outside the transmission of the data packet, in thefrequency channel concerned. The signal power SL1 which is determined ina frequency/time block outside the transmission of the respective datapacket can be defined, for example, by an external signal (interferencesignal) and/or by fading and/or by the background noise. The signalpower SL2 of the transmitting communication module can furthermore alsobe determined in a frequency/time block within the transmission of therespective data packet in the frequency channel concerned. Since thesignal power SL1 is determined outside the transmission of the datapacket, it can be defined whether a source of interference, i.e., forexample, an external signal transmission, is or is not present on thefrequency channel concerned. Here, a high signal noise on the frequencychannel also indicates a frequency channel affected by interference.Conversely, a low signal noise on the frequency channel normallyindicates a frequency channel unaffected by interference. This offersthe resulting advantage that, due to the detection of the signal powerSL1 on a frequency channel, the transmitter and/or receiver has thefacility to additionally check whether a successful transmission of thedata packets is or is not likely on this frequency channel. The datacollector can, for example, identify interference affecting thefrequency channels and can then transmit the information to theconsumption metering device indicating whether the frequency channelconcerned is or is not affected by interference.

The signal power SL1 outside the data packet and the signal power SL2during the transmission of the data packet are preferably placed inrelation to one another in order to define e.g. a signal-to-noise-ratioor a signal-to-interference-ratio. The interfering influence of thesignal noise on the transmission of the data packet can be determined,for example, on the basis of the signal-to-noise ratio and thetransmission quality on the frequency channel concerned can thus bedefined. Furthermore, it can thereby be determined whether the frequencychannel has a low signal noise due to transmission problems or fading orwhether noise signals have occurred.

The signal powers SL1 and/or SL2 and/or the relation between the signalpowers SL1 and SL2 can be used to fine-tune the likelihood ratio LR. TheLLR value can be scaled, for example, with the determined relationbetween the signal powers SL1 and SL2 in order to incorporate e.g. thesignal-to-noise ratio and/or the signal-to-interference ratio on therespective frequency channel also into the evaluation of thetransmission quality of the respective frequency channel. The frequencychannel selection is thereby improved to a substantial extent.

A mean value of the likelihood ratio LR of the bits or of a definednumber of bits of a data packet preferably serves as a metric fordetermining the interference state of the respective data packet. Astatement on the interference state of the data packet can thus be madein a simple manner.

The interference state of the data packet or parts thereof can beindicated here as a percentage value, as a decimal indication or as adual expression, e.g. as a binary numerical expression “0” or “1”, or asa decision expression “yes” or “no”.

A threshold value TV can appropriately be defined as a selectioncriterion or quality feature for the interference state of the datapacket, wherein the transmission quality of the respective frequencychannel is evaluated on the basis of the threshold value TV. A datapacket containing 12 bits, in which 3 bits have been rated as good(bit 1) and 9 bits have been down rated (bit 0) can be rated with theexpression 25% bit 1/75% bit 0, so that the interference state of thedata packet lies at 25%. With a threshold value TV=50%, the interferencestate of the data packet can thus be indicated as “no”, “affected byinterference” or “0”. Consequently, the evaluation of the transmissionquality of the frequency channel would also be indicated on the basis ofthis data packet e.g. as “no”, “affected by interference” or “0”. Aplurality of interference states of data packets which have beentransmitted via one frequency channel could furthermore also be used asa basis for evaluating the transmission quality of this frequencychannel. This can be done in a simple manner by averaging theinterference states of the data packets.

A plurality of frequency channel patterns comprising a respectivelydefined sequence of occupancy of the frequency channels is preferablyprovided. A frequency channel pattern can either extend here over allfrequency channels, i.e. every frequency channel is used for thetransmission of the data packets (full diversity), or it can be providedto eliminate specific frequency channels. A center-weighted frequencychannel pattern, for example, can eliminate all peripheral frequencychannels (high and low frequency ranges) for the transmission of thedata packets. Alternatively, all peripheral frequency channels can alsobe used in a frequency channel pattern for the transmission of the datapackets. Furthermore, only the frequency ranges of one side, i.e. eitherthe high or the low frequency ranges, can also be used for thetransmission of the data packets. For the transmission of a messageconsisting of a plurality of data packets, the data packets can alwaysbe transmitted in a specific frequency channel sequence, e.g. datapacket 1 via frequency channel 1, data packet 2 via frequency channel 2,data packet 3 via frequency channel 4, data packet 4 via frequencychannel 3, data packet 5 via frequency channel 1, etc. The frequencychannel pattern can be repeated here as often as required.

A change from the current frequency channel pattern to a differentfrequency channel pattern can appropriately be performed on the basis ofthe evaluation of the transmission quality of the respective frequencychannel.

An algorithm can furthermore be provided with which the transmitterchooses a frequency channel pattern which is communicated to thereceiver before or with the transmission of the data. The algorithm may,for example, be a random value or an event-based calculation.

The frequency channel pattern is preferably changed only if thetransmission quality of the new frequency channel pattern has beenverified. The verification can be performed e.g. by means of a frequencychannel sampling or a calibration function. This offers the resultingadvantage that no frequency channels or frequency channel patterns areselected which have a poor transmission quality.

A change signal can appropriately be generated by the transmitter inorder to signal an imminent change of the frequency channel pattern. Thechange signal must be acknowledged here by the receiver by means of anacknowledgement signal to the transmitter in order to enable a change ofthe frequency channel or of the frequency channel pattern. Theacknowledgement signal is generated by the receiver and is transmittedto the transmitter in order to permit a change of the frequency channelpattern. The communication between the transmitter and receiver isperformed here bi-directionally. This offers the resulting advantagethat no change of the frequency channel pattern takes place between thetransmitter and receiver without agreement on the new frequency channelpattern. As a result, the transmission situation or the evaluation ofthe frequency channel is also taken into account by the transmitter andreceiver for the selection of the frequency channel pattern. Thetransmission reliability in the selection of the frequency channels isthereby increased to a substantial extent. It is appropriate here if thechange signal of the transmitter already contains a frequency channelpattern proposed by the transmitter.

Alternatively or additionally, the acknowledgement signal can alsocontain a frequency channel pattern proposed by the receiver or istransmitted in the proposed frequency channel pattern, wherein thefrequency channel pattern thereby proposed by the receiver is thenverified by the transmitter and is rejected or accepted by thetransmitter on the basis of the verification.

The frequency channels can advantageously be sampled by transmitting afirst part of the data packets and/or a first part of the bits of a datapacket via specific frequency channels without a frequency channelchange. A second part of the data packets and/or a second part of thebits of a data packet are furthermore moved to other frequency channelsnot used for the data packet transmission in order to determine thetransmission quality of these frequency channels. The transmissionquality of the frequency channels on which the second part of the datapackets is transmitted can thereby be evaluated. Spectral gaps canfurthermore be identified through this step-by-step evaluation of thefrequency channels or frequency channel sampling (calibration function),and the transmission quality of the entire frequency band can thus beassessed. The evaluation of these frequency channels can also beincorporated into the selection of the frequency channels or frequencychannel patterns. This offers the resulting advantage that a broad rangeof frequency channels can be assessed for the frequency channelselection. All frequency channels of a frequency band are preferablysampled in the sampling of the frequency channels in order to determinethe optimum transmission quality within the frequency band.

The transmission quality of one frequency channel can also be evaluatedin a particularly advantageous manner on the basis of the evaluatedtransmission quality of other frequency channels or the interferencestate of a data packet which has been transmitted via a differentfrequency channel. This evaluation can be performed throughinterpolation, whereby e.g. the already performed evaluation of adjacentfrequency channels of a non-evaluated frequency channel provides anindication of how good the transmission quality of a non-evaluatedfrequency channel between the is, e.g. by averaging the interferencestate of the data packets which have been transmitted on the adjacentfrequency channels. Frequency channels can thereby be evaluated withoutdata packets or data packet parts having been transmitted via thesefrequency channels, so that the number of evaluated frequency channelsis increased with unvarying evaluation effort. The time required for theevaluation of the frequency channels can furthermore be reduced as aresult.

The transmitter and/or the receiver preferably comprise(s) a frequencyreference device for defining the frequency, wherein the frequencyreference devices normally have frequency deviations and the frequencydeviations are used to select and/or correct the frequency channel(s)and/or the frequency channel pattern.

Secondarily, the present invention claims a method which includes thefollowing method steps:

a) transmitting a data packet via a frequency channel from thetransmitter to the receiver;

b) receiving of the data packet by the receiver;

c) determining by the receiver, preferably bit-by-bit or group-by-groupfor specific bits, of the likelihood ratios LR of the data packet or fora defined part of the data packet;

d) estimating by the receiver of the frequency deviation of thefrequency reference device of the transmitter;

e) determining the interference state of the data packet on the basis ofthe likelihood ratios LR;

f) evaluating the transmission quality of the respective frequencychannel on the basis of the interference state of the data packet;

g) selecting and/or correcting a frequency channel or a frequencychannel pattern on the basis of the evaluation result; and

h) communicating the chosen frequency channel and/or the chosenfrequency channel pattern from the receiver to the transmitter.

A memory can appropriately be provided to store the evaluations of thetransmission quality of a frequency channel. The frequency channelsand/or the frequency channel pattern is/are additionally selected on thebasis of the stored evaluations.

It is particularly appropriate if a quality indicator QI which is usedfor the evaluations of the respective frequency channel pattern isdetermined on the basis of the evaluation of the frequency channelsand/or the interference state of the data packet or of a part of thedata packet, and the frequency channel pattern is selected on the basisof the quality indicator QI.

According to one particular design variant of the method, thetransmitter and/or the receiver may be a consumption metering device torecord the consumption data or a data collector to collect theconsumption data. The communication system serves here to transmit theconsumption data from a plurality of consumption metering devices to oneor more data collectors. The data collector(s) can then transmit theseconsumption data to a higher-level central unit of the provider.Furthermore, operational data, such as e.g. firmware updates, can alsobe distributed via the communication system to the consumption meteringdevices.

The calibration function is preferably performed using the downlinkmethod, i.e. the data collector transmits the data packets to theconsumption metering device for the evaluation of frequency channels.The transmit frequency and the receive frequency are used here only forthe transmission between these two transmitter and receivercommunication modules. Alternatively, however, the calibration functioncan also be performed using the uplink method, in which e.g. therespective consumption metering devices transmit data packets to thedata collector. For this purpose, the data collector must record thetransmission of all consumption metering devices on one frequencychannel. In particular, it is correspondingly advantageous for theuplink method to define specific times, referred to as timeslots, forthe transmission of the data packets from the consumption meteringdevices to the data collector on specific frequency channels in order toimplement a time division of the transmission of the data packets.Interference which could occur due to the simultaneous transmission of aplurality of consumption metering devices can thereby be avoided.

In an alternative design variant of the method, the transmitter is anapparatus for determining a content level. An apparatus of this typecould be provided, for example, on a garbage bin to determine thecontent level of the garbage bin, a water reservoir to determine thewater level (e.g. drinking water reservoir, drainage system or stormoverflow), a shelf (e.g. to store goods in daily use, documents ormedicines) to determine the storage quantities, or a different storagecontainer (e.g. a refrigerator or the like) to determine the contentlevel of the items stored in the storage container.

Secondarily, the present invention claims a method in which thefrequency channel(s) and/or the frequency channel pattern is/areselected on the basis of a random value. The random value can be definedhere e.g. randomly, pseudo-randomly or by a definable algorithm. Thetransmitter “rolls the dice”, for example, to obtain the random value bymeans of a specific encryption mechanism, thereby generating a randomfrequency channel pattern on the basis of randomly chosen frequencychannels, in particular from the already positively evaluated frequencychannels. The random value is transmitted in each case to the receiverbefore the data transmission so that the receiver can determine orcalculate the selection of the frequency channels or frequency channelpattern by the transmitter on the basis of the random value.

The selection can appropriately be made once more on the basis of therandom value with each subsequent data transmission or at specific timeintervals. As a result, new frequencies or frequency channel patternsare always selected, so that the transmission quality is improved to aparticular extent. Furthermore, it has surprisingly become evident thattransmission reliability is improved since e.g. attacks on thecommunication system by third parties are substantially hindered as aresult of the random and frequently performed variation of the frequencychannels or the frequency channel pattern.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method for selecting frequency channels, it is nevertheless notintended to be limited to the details shown, since various modificationsand structural changes may be made therein without departing from thespirit of the invention and within the scope and range of equivalents ofthe claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a simplified schematic view of a plurality of consumptionmetering devices which in each case transmit data packets to a datacollector by a communication module;

FIG. 2 is a simplified view of a temporal sequence of a transmission ofa data packet with low signal noise before and after the data packet;

FIG. 3 is a simplified view of the temporal sequence of the transmissionof a data packet with significant signal noise before and after the datapacket;

FIG. 4 is a simplified view of the temporal sequence of the transmissionof a data packet with an interference signal in the signal noise beforethe data packet;

FIG. 5 is a simplified schematic view of a consumption metering devicewhich transmits data packets to a data collector by means of acommunication module using the method according to the invention;

FIG. 6 is an illustration showing an example of a frequency channelpattern using the frequency hopping method;

FIG. 7 is an illustration showing a frequency channel pattern from FIG.6 using the frequency hopping method with frequency channels affected byinterference;

FIG. 8 are illustrations of a plurality of possible frequency channelpatterns using the frequency hopping method;

FIG. 9 is a simplified view of the data packet error rate curve and thelikelihood ratio curve over the frequency channels of theinterference-affected frequency channel pattern from FIG. 7;

FIG. 10 is a first flow diagram for verifying the transmission qualityof a frequency channel;

FIG. 11 is a second flow diagram for changing the frequency channelpattern; and

FIG. 12 is a graph of a transmission sequence of a data transmissionfrom a transmitter to a receiver in a specific frequency channel patternwith frequency deviation on the transmitter side and the receiver side.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first,particularly to FIG. 1 thereof, there is shown a communication system inwhich a plurality of consumption metering devices 2 in each case with anintegrated communication module 20 communicate via a radio link with acommunication module 10 of a data collector 1. Here, the respectiveconsumption metering device 2 transmits data packets 4 or parts of thedata packets 4 via the communication module 20 to the communicationmodule 10 of the data collector 1. In order to guarantee an adequatereception of the data packets 4, the communication module 10 of the datacollector 1 contains an antenna 3. The data packets 4 contain, forexample, the consumption metering data of the respective consumptionmetering device 2, such as, for example, the meter reading, presentconsumption, temperature or the like. The data packets 4 are transmittedhere between the communication modules 10 and 20 via a radio link usingthe frequency hopping method. Depending on whether the respectiveconsumption metering device 2 and/or the data collector 1 is currentlytransmitting or receiving, the consumption metering device 2 and/or thedata collector 1 can be the transmitter or the receiver.

The data packets 4 are transmitted according to the frequency hoppingmethod electively via a plurality of different frequency channels K1-Kn.The respective data packet 4 or a defined part of the same is codedbefore transmission by the transmitter, e.g. the respective consumptionmetering device 2 and is decoded following reception by the receiver,e.g. the data collector 1. The transmission quality of the frequencychannels K1-Kn is evaluated, wherein, on the basis of the evaluation ofthe transmission quality of the frequency channels K1-Kn, a decision ismade in respect of a selection of the frequency channel K1-Kn orfrequency channels K1-Kn which is/are used to transmit the data.According to the invention, a likelihood ratio LR for the likelihood ofa successful transmission is preferably determined bit-by-bit for thedata packet 4 or part of the same before the decoding by the receiver.The likelihood ratio LR can furthermore also be determined for adefinable group of bits. The respective likelihood ratios LR of the datapacket 4, of a part thereof, of the bits or of a group of bits are thenused as a metric for determining the interference state of the datapacket 4, wherein the transmission quality of the respective frequencychannel K1-Kn is evaluated on the basis of the interference state of thedata packet 4 or of a part of the data packet 4.

The likelihood ratio LR is calculated on the basis of the likelihoodratio test. A forward error correction (FEC) which makes it possible tocorrect the receiver is normally carried out in radio communicationsystems. As a result, for example, the range of the radio communicationsystem is increased. The likelihood ratios (LRs) which can be recordede.g. by an LLR module (not shown in the figures) are fed in at the inputof the receiver or decoder. If, for example, a data packet 4 made up ofbits or a part of the data packet 4 is severely affected byinterference, the data packet 4 or the part is down rated, e.g. in theworst case to 50% bit 1/50% bit 0 (i.e. 50% of the bits are affected byinterference and 50% of the bits are unaffected by interference). Thisdata packet 4 thus supplies no information or no reliable information.Conversely, a data packet 4 unaffected by interference can accordinglybe rated as good at e.g. 99% bit 1/1% bit 0. This likelihood ratio LRcan be determined for the data packet 4, a part of the data packet 4,each bit or a group of bits of the data packet 4. A likelihood ratio LR,for example, for a data packet comprising e.g. 12 bits can be determinedon the basis of the likelihood ratios LR of the bits in that e.g. 4 bitshave an LR=50%/50%, 4 bits an LR=100%/0% and 4 bits an LR=75%/25%. Thelikelihood ratio LR of the data packet 4 can be correspondinglycalculated according toLR=(0.33*0.5)+(0.33*1.0)+(0.33*0.85)=0.78(=78%).

A value of 50%, for example, corresponds here to a down rating, i.e. adeficient or interference-affected transmission, and a value of 99%, forexample, corresponds to a positive rating, i.e. a very good transmissionunaffected by interference. The likelihood ratio LR can furthermore alsobe used as a numerical measure (metric) for evaluating the transmissionquality of the entire frequency channel K1-K6. The data are distributedhere in data packets 4 or parts thereof (hops) on a plurality offrequencies or frequency channels K1-K6, wherein a likelihood ratio LRis calculated for each data packet 4 or a part of the data packet. Aplurality of data packets 4 which have been transmitted via the samefrequency are used to create a frequency metric (frequency evaluation).If no data packets 4 are transmitted on specific frequencies, thequality of these frequencies can alternatively be estimated throughinterpolation.

To select the frequency channels, the signal power SL1, for example, canbe determined in a frequency/time block 5 a outside the respective datapacket 4 in the relevant frequency channel K1-Kn. FIG. 2 shows thetemporal sequence of the transmission of a data packet 4 and the signalpower SL1 or the signal noise before and after the transmission of thedata packet 4. In order to define the signal power SL1, said signalpower can be averaged, for example, over the entire frequency/time block5 a or can be defined via the maximum and minimum signal power withinthe frequency/time block 5 a. The signal power SL1 outside thetransmission of the data packet 4 is substantially lower here than thesignal power SL2 during the transmission of the data packet 4.

FIG. 3 similarly shows a temporal sequence of the transmission of a datapacket 4. However, the signal power SL1 outside the transmission of thedata packet 4 or within the frequency/time block 5 b shows a significantdeviation which no longer differs substantially from the signal powerSL2 during the transmission of the data packet 4. The signal power SL1or the signal noise in the frequency/time block 5 b is thussubstantially higher than the signal power SL1 within the frequency/timeblock 5 a in FIG. 2.

The signal power SL1 in the frequency/time block 5 a indicates that verylittle or no interference has occurred or only a few or no externaltransmissions have taken place on the corresponding frequency channelK1-Kn at this time t. Consequently, the frequency channel K1-Kn appearsto be affected by little or no interference. In contrast, thefrequency/time block 5 b shows a significantly greater signal power SL1,thereby indicating a high proportion of interference and/or a lowtransmission quality. Similarly, according to FIG. 4, time-limitedand/or occasionally occurring interference can be identified bymeasuring it in a frequency/time block 5 c outside the transmission ofthe respective data packet 4.

Findings of this type can appropriately also be incorporated into theevaluation of the transmission quality of the frequency channels K1-Kn.A limit value, for example, for the signal power SL1 can also be definedin a frequency/time block 5 a, 5 b, 5 c outside the respective datapacket 4 of the relevant frequency channel K1-Kn. The currentlydetermined signal power SL1 within a frequency/time block 5 a, 5 b, 5 coutside the respective data packet 4 is constantly compared with thispredefined limit value. If the limit value is exceeded, the respectivedata packet 4 and/or the respective frequency channel K1-Kn is evaluatedas affected by interference. Not only uniformly increased signal powersSL1 outside the transmission of the data packet 4 (e.g. an increasedsignal noise according to the signal power SL1 in FIG. 3), but alsooccasionally occurring interference signals (e.g. interference accordingto the signal power SL1 in FIG. 4) are taken into account here in orderto detect different types of interference in a targeted manner.

Alternatively or additionally, the signal power SL2 during thetransmission of the data packets 4 and the signal power SL1 outside thetransmission of the data packets 4 can also be placed in relation to oneanother, i.e. a signal-to-noise and/or signal-to-interference ratiois/are determined. The respectively determined ratio can provideindications, inter alia, of the transmission quality of the data packets4 on the respective frequency channel K1-Kn. The decisive factor here isnot necessarily how great or small the signal noise SL1 outside thetransmission of the data packets 4 is, but rather how much greater thesignal power SL2 during the transmission of the data packets 4 iscompared with the signal power SL1 outside the transmission of the datapackets 4. Different influences on the transmission quality, such ase.g. fading caused by poor transmission conditions at the site (e.g.caused by shadowing) can thereby also be determined and distinguished.The frequency channels K1-Kn are thereby evaluated even more reliably byscaling the interference state of the data packets 4 or the likelihoodratio LR with the signal-to-noise and/or signal-to-interference ratiosof the respective data packets 4, i.e. the signal-to-noise ratio or thesignal-to-interference ratio is taken into account in the likelihoodratio calculation.

FIG. 5 shows the communication system from FIG. 1 with a consumptionmetering device 2 and interference 5 in the vicinity of the consumptionmetering device 2. If interference 5 occurs in the vicinity of afrequency channel K1-Kn which is used for the transmission of the datapacket 4 from the communication module 20 of the consumption meteringdevice 2 to the communication module 10 of the data collector 1, theconsumption metering device 2 or its communication module 20 canestablish e.g. on the basis of an interference detection thatinterference 5 is present. An interference detection based on thelikelihood ratio LR, for example, can also be used. In order to theneffect a frequency channel changeover, it is advantageous according toone appropriate design if the consumption metering device 2 transmits achange signal 6 which is generated by the communication module 20 viathe communication channel 20 to the communication module 10 of the datacollector 1. After the communication module 10 has received the changesignal 6 from the communication module 20, the communication module 10verifies the change request for the frequency channel K1-Kn from thecommunication module 20. In order to effect the change of the frequencychannel K1-Kn, the communication module 10 of the data collector 1generates an acknowledgement signal 7 which the communication module 10transmits to the communication module 20. The frequency channel K1-Kn orthe entire frequency channel pattern 8, 8 a-8 d can then be changed bythe communication module 20 or 10. The change of the frequency channelpatterns 8, 8 a-8 d can thereby be controlled in such a way that a newfrequency channel pattern 8, 8 a-8 d is selected only if it has beenverified in terms of transmission quality. The transmission quality canbe verified e.g. by means of a frequency channel sampling or by means ofthe calibration function.

FIG. 6 shows a simplified view of a frequency channel pattern 8 usingthe frequency hopping method. The data packets 4 are transmitted herewith a time delay via the frequency channels K1-K6 between thecommunication modules 10, 20. All frequency channels K1-K6 within thefrequency channel pattern 8 are used for the transmission of the datapackets 4 (full diversity). If interference 5 occurs in the frequencychannels K3 and K4, according to FIG. 7, the data packets 4 which aretransmitted via the frequency channels K3 and K4 can no longer betransmitted without interference. A loss or partial loss of these datapackets 4 would be the consequence. In the method according to thepresent invention, this interference can be detected in a timely mannere.g. by means of an interference detection already described. Due to achange of the frequency channels K1-K6 to be transmitted or of theentire frequency channel pattern 8, it is guaranteed that even the datapackets 4 affected by interference or their interference-affected partscan similarly be transmitted without interference if they aretransmitted via the other frequency channels K1, K2, K5 and K6.

The frequency channel pattern 8 according to FIG. 6 and FIG. 7 can bechanged to the frequency channel pattern shown in FIG. 8. The frequencychannel pattern 8 a shows a peripheral weighting of the frequencychannels K1-K6. The frequency channels K3 and K4 are eliminated here.The frequency channel pattern 8 a can be used accordingly if the middlefrequency ranges K3 and K4 are affected by interference. Alternatively,in the case of peripheral interference affecting e.g. the frequencychannels K1, K2, K5, K6, the frequency channel pattern 8 b can be used,in which a center-weighted measurement of the frequency ranges or thefrequency band is performed via the frequencies K3 and K4. In the caseof unilateral peripheral interference, i.e. interference in either theupper or lower frequency range, the respective interference-affectedfrequency range is eliminated. According to the frequency channelpattern 8 c, the lower frequency range within which the frequencychannels K1-K3 lie, is correspondingly eliminated. The data packets 4are transmitted here only via the frequency channels K4-K6 of the upperfrequency range. The frequency channel pattern 8 d also shows atransmission of the data packets 4 in the lower frequency range via thefrequency channels K1-K3, wherein the frequency channels K4-K6 which liewithin the upper frequency range are eliminated for the transmission ofthe data packets 4.

The likelihood ratios LR of the frequency channels K1-K6 can preferablybe plotted as the likelihood ratio curve 11 over the frequency channelsK1-K6. The likelihood ratio curve 11 of the likelihood ratios LR for thefrequency channels K1-K6 of the interference-affected frequency channelpattern 8 according to FIG. 7 is represented graphically in FIG. 9.According to FIG. 9, the likelihood ratio LR is highest for channels K1and K6 and lowest for channels K3 and K4. The frequency channels K3 andK4 are consequently to be evaluated as affected by interference.

A data packet error rate (hop error rate) can furthermore be defined foreach frequency channel K1-Kn, e.g. on the basis of the interferencedetection and the signal-to-noise ratio on the respective frequencychannel K1-Kn. The data packet error rate curve 12 for the frequencychannels K1-K6 according to the interference-affected frequency channelpattern 8 in FIG. 7 is similarly shown in FIG. 9. It is similarlyevident here that the frequency channels K3 and K4 which have a highdata packet error rate are unsuitable for a transmission of the datapackets 4. The frequency channels K1 and K6 which have a low data packeterror rate are furthermore highly suitable for the transmission of thedata packets 4. It is evident here also that a frequency channelchangeover should take place in such a way that the peripheral frequencychannels K1, K2, K5 and K6 which are suitable for a data transmission ofthe data packets 4 are used for the transmission of the data packets 4.This evaluation of the frequency channels K1-K6 is defined here by thedata packet error rate and the likelihood ratio LR. The reliability ofthe selection of the frequency channels K1-K6 is increased to aconsiderable extent by this double evaluation.

The likelihood ratio LR of the data packet 4 can be represented eitherby the indication of whether the data packet 4 is or is not affected byinterference, or precisely as a numerical value or percentageexpression. If the likelihood ratio LR is indicated as a dualexpression, e.g. “0” and “1”, the frequency channel K1-K6 is to becategorized as in good order as soon as the sum of the likelihood ratiosis LR>0 (e.g. two thirds of the bits are in good order).

A selection for a frequency channel pattern (“Hop metric”) can be madeon the basis of the percentage representation through an averaging ofthe interference states of the data packets 4 or their parts or thelikelihood ratios LR. A quality indicator QI is preferably defined orcalculated for the evaluation of the respective frequency channelpattern 8, 8 a-8 d. The calculation is performed e.g. via the averageweighting of the data packets 4 or their interference states. Forexample, 25% of the data packets 4 can be weighted at 50% (completelyaffected by interference), 25% at 60% (slight tendency) and 50% at 98%(virtually unaffected by interference). The quality indicator QI for thefrequency channel is calculated here according toQI=(0.25*0.5)+(0.25*0.6)+(0.5*0.98)=0.765(=76.5%).

A limit value LV of the quality indicator QI can furthermore be definedfor the decision as to whether a frequency channel pattern 8, 8 a-8 d isor is not used, e.g. 70%, preferably 75%, particularly preferably 80%.The currently calculated quality indicators QI of the respectivefrequency channel patterns 8, 8 a-8 d can then be compared with thelimit value of the quality indicator QI, wherein the current frequencychannel pattern 8, 8 a-8 d is changed to a different frequency channelpattern 8, 8 a-8 d which has the highest possible quality indicator QIif the limit value of the quality indicator QI is understepped.

In the case where specific frequencies or frequency channels K1-K6 areaffected by interference, a new frequency channel pattern 8, 8 a-8 d canthus be selected. If the receiver wishes to change the frequency channelpattern 8, 8 a-8 d, the receiver can either itself decide whichfrequency channel pattern 8, 8 a-8 d is set, inform the transmitterwhich frequency channel pattern 8, 8 a-8 d is intended to be set orleave the decision to the transmitter. An “agreement” is preferably madehere between the transmitter and the receiver (“ping-pong”).

Alternatively or additionally, the number of received data packets 4that are unaffected by interference can also be used for the evaluationof the frequency channel pattern 8, 8 a-8 d. To do this, the number ofinterference-unaffected data packets 4 which is required in order tosuccessfully decode the entire data message is compared with the numberof received interference-unaffected data packets 4. If the number ofreceived interference-unaffected data packets 4 is less than the numberof required data packets 4, the frequency channel K1-Kn or the frequencychannel pattern 8, 8 a-8 d is evaluated as affected by interference.This can be done automatically, for example, by means of a forward errorcorrection (FEC) which serves to reduce the error rate in thetransmission of the data packets 4. The data packets 4 to be transmittedby the transmitting communication module 10 or 20 are coded in aredundant manner in a transmission system so that the receivingcommunication module 10 or 20 can detect and correct transmission errorswithout an inquiry to the transmitting communication module 10 or 20.

FIG. 10 shows one design of a flow diagram for verifying thetransmission quality of a frequency channel K1-Kn. The signal-to-noiseratio or the signal-to-interference ratio is preferably first determinedfor the data packet 4 arriving at the receiver. The likelihood ratio LRis furthermore preferably determined bit-by-bit in order to identify theinterference state of the data packet 4. A threshold value TV (e.g. 75%)is then defined for the interference state. The signal-to-noise ratio orsignal-to-interference ratio can furthermore be used to determine thelikelihood ratio LR, i.e. the likelihood ratio LR is defined and scaledwith the signal-to-noise ratio or signal-to-interference ratio. Aquality indicator QI can then be determined for the respective frequencychannel pattern 8, 8 a-8 d as described above on the basis of thelikelihood ratios LR of the bits or of the data packets 4. The frequencychannel pattern 8, 8 a-8 d is then evaluated as unaffected byinterference if the quality indicator QI is greater than the limit valueLV.

The flow diagram according to FIG. 10 can be performed continuously foreach data packet 4 or parts of the same, on a random basis for specificdata packets 4 or as part of the frequency channel sampling or thecalibration function. The transmission quality of a frequency channelpattern 8, 8 a-8 d can be determined here by transmitting and verifyingall of the data packets 4 of a frequency channel pattern 8, 8 a-8 d(e.g. eight data packets 4 according to FIGS. 6-8) at least once on thecorresponding frequency channels K1-K6. Some of the data packets 4 orhops, for example, remain on their frequency channel while other datapackets 4 are transmitted on alternative frequencies or other frequencychannels in order to test these frequencies or frequency channels. Theentire frequency band can thereby be sampled, as a result of which gapsin the spectrum can be identified and can then be closed e.g. throughinterpolation.

FIG. 11 shows one design of a flow diagram for changing the frequencychannel pattern 8, 8 a-8 d. The first step of the flow diagram entailsdetermining or defining a limit value LV for the number of transmittedinterference-unaffected data packets 4 which is required in order to beable to successfully decode the data packets 4, or for the qualityindicator QI, e.g. 10%. If the number of actually received data packets4 or the quality indicator QI is above the limit value LV, no change ofthe frequency channel pattern 8, 8 a-8 d is required. If the number ofactually received data packets 4 or the quality indicator QI is belowthe limit value LV, a change of the frequency channel pattern 8, 8 a-8 dis required. For this purpose, a verification of the transmissionquality of the data packets 4 on the corresponding frequency channelsK1-Kn of the frequency channel pattern 8, 8 a-8 d to be set is firstcarried out according to the flow diagram in FIG. 10. The frequencychannel pattern 8, 8 a-8 d is consequently verified before a change tothis frequency channel pattern 8, 8 a-8 d takes place. If the number ofexpected interference-unaffected data packets 4 determined here is abovethe limit value LV (e.g. 99%/bit 1 and 1%/bit 0), the respectivefrequency channel pattern 8, 8 a-8 d can be selected, for example, bythe transmitter and/or receiver. If the determined number of expectedinterference-unaffected data packets 4 is below the limit value LV (e.g.50%/bit 1 and 50%/bit 0), a new frequency channel pattern 8, 8 a-8 d isverified by means of the flow diagram according to FIG. 10 and isselected once more in the event of corresponding transmission quality.The flow diagram according to FIG. 11 is preferably repeated until afrequency channel pattern 8, 8 a-8 d which has at least a sufficientlygood transmission quality has been determined.

FIG. 12 shows a data transmission in which the transmitter and thereceiver have first agreed at time t(now) on the frequency channelpattern indicated in FIG. 12 with black data packets 4, wherein the datapackets 4 (or only parts thereof) are transmitted via the frequencychannels K1-K6 in the temporal sequence shown. However, due todeviations in the frequency reference devices of the transmitter andreceiver, e.g. the consumption metering device 2 and the data collector1, the set frequency channel pattern or the set frequency channels maydiffer after a certain time period at time t(later) on the transmitterside and on the receiver side, as shown in FIG. 12 on the basis of thewhite data packets. The transmit frequency may, for example, shift by 5kHz or the like, so that the data transmission would no longer besuccessful.

In order to avoid this problem, the data collector 1 can, for example,also take account of the error of the frequency reference device of theconsumption metering device 2 in the selection of the frequency channelK1-Kn or the frequency channel pattern 8, 8 a-8 d. The data collector 1can, for example, estimate the error of the frequency reference deviceof the consumption metering device 2 (e.g. a crystal error of 5 ppm, 5kHz or the like) and can already incorporate it into the frequencychannel.

Individual feature combinations (sub-combinations) and also possiblecombinations of individual features of different design forms not shownin the figures in the drawing are also expressly comprised by thecontent of the disclosure.

The following is a summary list of reference numerals and thecorresponding structure used in the above description of the invention:

-   1 Data collector-   2 Consumption metering device-   3 Antenna-   4 Data packet-   5 Interference-   5 a Frequency/time block-   5 b Frequency/time block-   5 c Frequency/time block-   6 Change signal-   7 Acknowledgement signal-   8 Frequency channel pattern (full diversity)-   8 b Frequency channel pattern (center-weighted)-   8 a Frequency channel pattern (periphery-weighted)-   8 c Frequency channel pattern (in the high frequency range)-   8 d Frequency channel pattern (in the low frequency range)-   10 Communication module-   11 Likelihood ratio curve-   12 Data packet error rate curve-   20 Communication module-   K1-Kn Frequency channels-   LR Likelihood ratio-   QI Quality indicator-   SL1 Signal power outside the transmission of the data packets-   SL2 Signal power during the transmission of the data packets-   t Time-   LV Limit value-   TV Threshold value-   DR Data packet reliability

The invention claimed is:
 1. A method for selecting frequency channelsin a communication system using a frequency hopping method, in whichdata are transmitted between a transmitter and a receiver by means ofradio transmission, which comprises the steps of: transmitting the datain parts of data packets in a frequency/time block; providing aplurality of different frequency channel patterns, each frequencychannel pattern having a defined sequence of occupancy of the frequencychannels; transmitting the parts of the data packets electively via theplurality of different frequency channel patterns, wherein a respectivedata packet or parts of the respective data packet are coded beforetransmission by the transmitter and are decoded after reception by thereceiver; evaluating a transmission quality of the frequency channelsand, on a basis of an evaluation of the transmission quality of thefrequency channels, a decision is made in respect of a selection of atleast one frequency channel pattern which is used to transmit the data,receiving the data packet by the receiver; determining a likelihoodratio LR of a part of a data packet by the receiver; determining aninterference state of the part of the data packet on a basis of thelikelihood ratio LR of the part of the data packet; evaluating thetransmission quality of a respective frequency channel on a basis of theinterference state of the part of the data packet; selecting and/orcorrecting the respective frequency channel pattern on the basis of anevaluation result; and communicating a selected and/or correctedfrequency channel or frequency channel pattern from the receiver to thetransmitter.
 2. The method according to claim 1, which furthercomprises: providing a memory to store evaluations of the transmissionquality of the frequency channel; and selecting the frequency channelsand/or the frequency channel pattern on a basis of stored evaluations.3. The method according to claim 1, which further comprises determininga quality indicator QI used to evaluate a respective frequency channelpattern on a basis of the evaluation of the transmission quality of thefrequency channels and/or the interference state of the data packets. 4.The method according to claim 1, wherein at least one of the transmitteror the receiver is a consumption metering device to record consumptiondata or a data collector to collect the consumption data.
 5. The methodaccording to claim 1, wherein the transmitter is an apparatus fordetermining content level.
 6. A method for selecting frequency channelsin a communication system using a frequency hopping method, in whichdata are transmitted between a transmitter and a receiver by means ofradio transmission, which comprises the steps of: transmitting the datain parts of data packets in a frequency/time block; providing aplurality of different frequency channel patterns, each frequencychannel pattern having a defined sequence of occupancy of the frequencychannels; transmitting the parts of the data packets electively via aplurality of different frequency channels, wherein a respective datapacket or the parts of the respective data packet are coded beforetransmission by the transmitter and are decoded after reception by thereceiver; evaluating a transmission quality of the frequency channelsand, on a basis of an evaluation of the transmission quality of thefrequency channels, a decision is made in respect of a selection of atleast one frequency channel pattern which is used to transmit the data;receiving the parts of the data packets by the receiver; determining alikelihood ratio LR of a part of a data packet by the receiver;estimating by the receiver a frequency deviation of a frequencyreference device of the transmitter; determining the interference stateof the part of the data packet on a basis of the likelihood ratio LR ofsaid part of a data packet; evaluating the transmission quality of arespective frequency channel on a basis of the interference state of thepart of the data packet; selecting and/or correcting the respectivefrequency channel pattern on the basis of said evaluation result andfrequency deviation; and communicating a selected and/or correctedfrequency channel pattern from the receiver to the transmitter.
 7. Themethod according to claim 6, which further comprises: providing a memoryto store evaluations of the transmission quality of the frequencychannel; and selecting the frequency channels and/or the frequencychannel pattern on a basis of stored evaluations.
 8. The methodaccording to claim 6, which further comprises determining a qualityindicator QI used to evaluate a respective frequency channel pattern ona basis of the evaluation of the transmission quality of the frequencychannels and/or the interference state of the data packets.
 9. Themethod according to claim 6, wherein at least one of the transmitter orthe receiver is a consumption metering device to record consumption dataor a data collector to collect the consumption data.
 10. The methodaccording to claim 6, wherein the transmitter is an apparatus fordetermining content level.